The present invention relates to a start control device including a compression self-ignition engine for combusting a fuel injected into a cylinder by self-ignition. The start control device automatically stops the engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarts the engine by injecting the fuel into a compression-stroke-in-stop cylinder that is on a compression stroke while the engine is stopped, while applying a torque to the engine by using a starter motor.
In recent years, compression self-ignition engines represented by a diesel engine have been widely familiarized as in-vehicle engines for reasons of their generally excellent thermal efficiency and less discharge amount of CO2 compared to spark-ignition engines, such as gasoline engines.
For larger reduction of CO2 in such compression self-ignition engines, it is effective to adopt the art of a so called idle stop control of automatically stopping the engine under, for example, an idle drive, and then automatically restarting the engine when, for example, a starting operation of the vehicle is performed, and various studies relating to this have been performed.
For example, JP2009-062960A discloses a control device of a diesel engine for automatically stopping the diesel engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarting the diesel engine by injecting a fuel while applying a torque to the engine by driving a starter motor. Further, it is disclosed that a cylinder into which the fuel is injected first is changeably set based on a stop position of a piston of a cylinder that is on a compression stroke while an engine is stopped, in other words, when the engine stop is completed (compression-stroke-in-stop cylinder).
Further specifically, when the diesel engine is automatically stopped, a position of the piston of the compression-stroke-in-stop cylinder that is on the compression stroke at that time is determined, and it is determined whether the piston position is within a predetermined reference stop position range set relatively on a bottom dead center (BDC) side. When the piston position is within the reference stop position range, in restarting the engine, the fuel is injected into the compression-stroke-in-stop cylinder first, and on the other hand, when the piston position is on a top dead center (TDC) side of the reference stop position range, when the engine overall passes the TDC for the first time in the restart and an intake-stroke-in-stop cylinder (cylinder on intake stroke while the engine is stopped) reaches the compression stroke, the fuel is injected into the intake-stroke-in-stop cylinder.
According to such a configuration, when the piston of the compression-stroke-in-stop cylinder is within the reference stop position range, by injecting the fuel into the compression-stroke-in-stop cylinder, the fuel can surely self-ignite and the engine can promptly be restarted in a comparatively short time period (referred to as “the first compression start” for convenience). On the other hand, when the piston of the compression-stroke-in-stop cylinder is located on the TDC side of the reference stop position range, because a compression stroke amount (compression margin) is less and a temperature of air inside the cylinder does not rise sufficiently, a misfire may occur even when the fuel is not injected into the compression-stroke-in-stop cylinder. Therefore, in such a case, the fuel is injected into the intake-stroke-in-stop cylinder and not the compression-stroke-in-stop cylinder, and thereby, the air inside the cylinder is sufficiently compressed and the fuel can surely self-ignite (referred to as “the second compression start” for convenience).
As described above, conventionally, when restarting the engine, it is determined whether the piston of the compression-stroke-in-stop cylinder is stopped within the reference stop position range, and when the piston is stopped therein, the fuel is injected into the compression-stroke-in-stop cylinder and the engine is promptly restarted by the first compression start.
Meanwhile, the engine restart condition is broadly based on requirements from a driver and others. The requirement from the driver includes a starting operation of the vehicle, such as a disconnecting operation of clutches and a release operation of a brake. The requirements from others include the occurrence of necessities of restarting the engine for a systematic reason, such as a necessity of activating an air conditioner, a decrease in battery voltage, and a long automatic stop time period of the engine (referred to as “the systematic requirement” for convenience). When the engine is restarted by the starting requirement from the driver, the driver knows in advance that the engine is to be restarted. Therefore, even if vibrations occur due to the restart, a person on board does not feel greatly uncomfortable. On the other hand, when the engine is restarted by the systematic requirement, the driver does not know in advance that the engine is to be restarted. Therefore, if the vibrations occur due to the restart, the person on board feels greatly uncomfortable and an NVH (noise, vibration, and harshness) degrades significantly.
Further, according to the studies by the present inventors, it has been found that if the engine is always restarted by the first compression start when the stop position of the piston of the compression-stroke-in-stop cylinder is within the reference stop position range so as to shorten a restart time period (the time period from the start of driving the starter motor to a complete explosion of the engine), comparatively large vibrations occur in the restart comparatively more frequently. It is considered that the frequent vibrations are influenced by a resonant frequency of the vehicle depending on combinations of components, such as the engine, an engine mount, a transmission, and a chassis.
The present invention is made in view of the above situations, and allows, when restarting a compression self-ignition engine, a selection of prioritization between a prompt start and the NVH according to a restart condition of the engine. Thus the engine is always restarted in a most suitable mode, thereby improving a start control device of the compression self-ignition engine.